The subject matter described herein relates generally to methods and systems for operating a wind turbine, and more particularly, to methods and systems for operating a control system for a wind turbine and to a wind turbine comprising such a control system.
At least some known wind turbines include a tower and a nacelle mounted on the tower. A rotor is rotatably mounted to the nacelle and is coupled to a generator by a shaft. A plurality of blades extends from the rotor. The blades are oriented such that wind passing over the blades turns the rotor and rotates the shaft, thereby driving the generator to generate electricity.
Known wind turbines typically are designed and/or assembled with predefined rated power limits. To safely operate within such rated power limits, the electrical and/or mechanical components may be operated within certain operating limitations. In order to prevent early fatigue and wear of the wind turbine and its components threshold values for the mechanical and electrical components may not be exceeded.
For example, operating a wind turbine with a high rotational speed, typically results in high loads which may reduce the life time of the wind turbine and its components, respectively. Typically, a threshold value is set for the rotor speed of a wind turbine. Under certain conditions, such as high winds in the area of the wind turbine or when a failure of the drive system occurs or when the wind turbine is in an uncontrolled condition, the rotor speed may eventually exceed this threshold value.
At least some known wind turbines are designed for regulating the rotor speed of the wind turbine within a certain speed range in order to minimize the events of exceeding the threshold values.
At least some known wind turbines are designed for regulating the rotor speed within the threshold value by reducing the rotor speed or initiating an emergency shut-down.
An immediate decrease of the rotor speed, for example by mechanical braking, may result in a particularly significant increase of the load acting on components of the wind turbine. Generally, such a significant load increase negatively influences the operating lifetime of the turbine. Moreover, alternating forces may excite the resonant modes of the tower and lead to a resonant vibration of the tower. Such a resonant vibration of the tower may require shutting down the wind turbine. As a result, a loss of the capacity for generating power by the wind turbine is caused and a trip of the service staff to the wind turbine might be necessary.
Accordingly, it is desirable to provide a method and an apparatus capable of operating a wind turbine so that high loads on the wind turbine components are prevented and at the same time the number of emergency shut-downs of the wind turbine is reduced.